Connection error

An unexpected error occurred.

UNKNOWN_CONNECTION_ERROR

Symptoms

  • The error banner shows a generic "Connection error" without a specific cause.
  • The technical details show a raw message MCUHex did not recognize.

Likely causes

  • A raw probe or pyOCD error that does not match any known pattern.
  • An unusual combination — exotic probe firmware, adapters, or OS-level USB quirks.

How to fix it

  1. Run the standard triage

    Replug the probe, restart the SDK, refresh the page, retry. This clears most one-off failures.

  2. Read the technical detail

    Expand the error’s technical message — it often names the real cause (permissions, busy, timeout) even when unclassified. Then follow the matching guide on this site.

  3. Report it

    If it reproduces, send us the technical message via the feedback form — unrecognized errors we see get promoted into first-class guides here.

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